During the early development of D. melanogaster a single egg cell is converted into a multicellular organism (the first instar larva) which contains in a defined spatial arrangement a variety of specialized organs, tissues, and cell types. Our research focuses on one aspect of embryogenesis which is particularly amenable to study in D. melanogaster - the role of, and the mechanisms controlling differential gene expression during embryogenesis. Two question are of special interest: 1) is there a temporal coordination between a 'program' of gene expression and the differentiation of specific tissues or cell types during embryogenesis? and 2) if so what are the mechanisms involved that result in coordinate gene expression? As a first step in answering these questions we have investigated a relatively simple system, heat shock, which shows an apparently coordinate response of a limited number of genes to environmental manipulations. A number of genes induced by heat shock have been isolated, and the structure and organization of these genes is being studied. We have been able to identify a number of common structural features which may account for the coordinate induction of a number of these genes. Using a similar approach we have identified recombinant DNAs corresponding to genes which are expressed as mRNA during early embryogenesis. We are currently examining the structure of these genes as well as their temporal pattern of expression.